Saturday, November 17, 2012

Easy on the Ivy

There may be many evils in the universe, greed, sloth, Darth Vader, etc.  Now a letter in the Daily Telegraph would have us believe there is another far greater – ivy!  Read on:  “SirApart from the small number of property owners who have eradicated this plague, a look at the countryside reveals that trees are being strangled by ivy.  It is now spreading horizontally across verges, woodland, and wasteland.  Something must be done about it”.
Wow, but before we launch our slash and burn assault let us have a glance at the case for the defence.  Ivy does not cause trees to die.  It is a non-parasitic climber, taking no nutrients from any trees it uses as support.  If it needed to take nutrients from what supported it then clearly it could not grow up walls.  The adhesive hairs on its stems are for grip only, and while they may scour masonry they do not harm tree bark in any way.
Ivy has its own roots and leaves, photosynthesising food and taking up water itself.  Its roots are not deep and hardly compete with its host tree more than any other plants in the vicinity.  Its leaves are along branches and trunks, grabbing what sunlight passes through gaps in the tree’s crown, it certainly does not shade sunlight from the tree.  Indeed it is not in its interest to out-compete and ‘strangle’ its supporting tree to death, otherwise it would be brought down with it itself.
It may come as a shock to the letter’s writer but trees do die, and maybe the sight of living ivy still clinging to a dead tree may suggest a connection.  It is well to recall the adage ‘correlation does not imply causality’, for it is particularly poignant here. 
Ivy also has great ecological significance as one of nature's larders and dormitories.  It flowers and produces nectar late in the year when other sources are scarce, a blessing for many insects.  Its berries remain through to February and are a vital source of winter food for birds.  Being evergreen it is also a valuable year-round home and roost for a whole range of creatures from invertebrates to mammals. 
It may often look untidy, it may sometimes be ‘framed’ when its support tree dies, but far from ‘doing something about it’ it would be better if we left it alone and just enjoyed the wildlife that it sustains.
Ivy growing up a telegraph pole (which was once a Scot's Pine but definitely not killed by the ivy!)

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